1. Field of the Invention
The present invention relates to an operation control method for a hand-carried engine-driven working machine such as lawn mower or a chain saw.
2. Description of the Related Art
In hand-carried engine-driven working machines which are currently marketed, carburetors of engines are adjusted to correct a variation in performance for optimum engine driving before shipment from an engine assembly plant.
Regardless of the adjustment made by manufacturers, the optimum fuel combustion within an engine varies depending on various conditions such as the temperature and atmospheric pressure in an environment where a working machine is used, the kind of fuel used, the running-in condition of the engine, and the condition of an air cleaner (that is, whether or not it is clogged), and consequently the optimum driving of the engine cannot be ensured any more, leading to a drawback of a deterioration of fuel economy, a reduction in output of the engine or an increase in exhaust emissions.
As a means for eliminating such a drawback, a user should adjust a needle valve of a carburetor for each work so as to control the supply of fuel for optimum combustion. However, an accurate adjustment of the needle valve requires skill of a high level and an exclusive facility. Namely, in the case of a normal engine, the user adjusts a needle valve of a carburetor while measuring the rotation speed of the engine to correct the air-fuel ratio which is changed by the working environment immediately after the engine is started. However, it is difficult to prepare a precision engine speed measuring device at an outside working site. Further, the vibration of the engine makes it difficult to precisely control the supply of fuel by rotating the needle valve accurately.
For example, Patent Literature 1 (JP-A-2011-012685) discloses a conventional technique which automatically controls a carburetor to properly deal with the change in working environment described above.
In the conventional technique described above, however, a relatively long period of time is necessary to stabilize the rotation speed of the engine, and hence, the conventional technique has a problem that it is not suitable for a case where the rotation speed of the engine changes due to an abrupt change in load in an actual working environment.